1. Field of Invention
The invention generally relates to a method of joining image, and in particular relates to a method applied in a scanner for joining the image data of a scanned document when the data in a register is full and the scanning is paused and resumed, the joining is prevented from being overlapped or broken.
2. Related Art
FIG. 1 is a schematic diagram of a conventional scanning device including a scanner 10 and a computer terminal 105. When scanning a document (not shown) being illuminated, a linear photodetector 101 gets scanning image signals of the document and transfers to an image processor 102. The image processor 102 converts the signals into digital signals (data) and stores into a register 103. With a protocol between a data-transfer interface 104 and the terminal 105, the image data is transferred from the register 103 to the terminal 105 and displayed.
However, since the transfer speed of image data from the image processor 102 to the register 103 is usually faster than that from the register 103 to the terminal 105, the image data stored in the register 103 is gradually full during the transfer. At a critical point, the image processor 102 has to stop a motor M1 and to stop the scanning of the linear photodetector 101. The motor M1 decelerates to stop the linear photodetector 101 so that the image data stored in the register 103 gets time to be transferred. After then, the motor M1 restarts to speed up the scanning of the linear photodetector 101 till a normal speed. After the pause and resuming, the broken image data portions have to be joined.
Since the motor M1 requires an acceleration time when restarting from still to a normal scanning speed, the linear photodetector 101 is first moved backward before restarting forward so as to resume scanning speed before reaching the position where it stopped scanning last time. By controlling the time of data acquiring when moving backward and forward, the scanning image data is supposed to be suitably joined.
However, caused by mechanical transmission deviation such as backlash of gears, the motor M1 and related transmission elements (not shown) usually make the scanning image data overlapped or broken after the backward and forward movements.
Therefore, there has been a scanning method that scans and stores image data during the backward movement. Then, compare the backward image data with the scanning image data when starting forward so as to get the matched portions for joining.
Still unfortunately, the aforesaid method fails when the scanning image data includes repeating portions.